A standard extruder nozzle is often equipped with its own heater so that it can be maintained at a precise temperature that is set to ensure that the resin being pumped through it remains fluent. The nozzle is an elongated metallic part that normally is centered on a central longitudinal axis. The heater is annularly tubular and fit closely around the nozzle.
To this end the heater is typically formed as a coil having a multiplicity of turns and a pair of ends projecting tangentially from the coil. A resistance-heating wire extends through the turns to heat them.
In order to maximize heat transfer from the tubularly annular heater to the outer surface of the nozzle, the heater is clamped tightly on the nozzle. This can be done as described in German patent 3,736,612 by a mounting sleeve that fits tightly around the heater and that is provided with a wedge arrangement that projects radially and that is traversed by a longitudinal screw that can be tightened to pull the sleeve tightly around the heater and compress it radially inward on the nozzle.
Such an arrangement has the considerable disadvantage that the mounting sleeve itself, at least the radially projecting clamping part, is fairly bulky. It must be accommodated in the extruder by special orientation of the nozzles or formation of the extruder. What is more it normally creates a location where the thermal characteristics are different from the rest of the nozzle, forming a hot or cold spot, because the rest of the mounting sleeve is either exposed or in contact with the extruder. Finally mounting this sleeve requires the use of tools, and taking it off not only also requires tools, but is frequently very difficult because it has frozen in place on the heater coil.